Process for the production of high-purity isobutene through the cracking of MTBE or ETBE and integrated process for the production of the relative ether

Abstract

Process for the production of high-purity isobutene starting from a stream prevalently containing MTBE (Methyl-Tert Butyl Ether) or ETBE (Ethyl-Tert Butyl Ether) which essentially comprises the following areas in sequence: • a fractionation area for obtaining a stream of high-purity MTBE or ETBE; • a cracking area of said stream of MTBE or ETBE for obtaining an outgoing stream prevalently containing isobutene and the relative alcohol, methanol or ethanol; • a washing area with water of the stream leaving the cracking area for the recovery of the relative alcohol, in order to obtain a stream containing isobutene, the ether fed and light compounds and a stream substantially consisting of water and relative alcohol, with a relevant fractionation section for separating the washing water to be recycled to the same washing area from the relative alcohol; • a fractionation area of the stream containing isobutene, the ether fed and light compounds for separating a stream of high-purity isobutene. The process can be possibly integrated with a process for the production of MTBE or ETBE.

The invention claimed is: 
     
       1. A process for the production of high-purity isobutene which comprises feeding a stream containing MTBE (Methyl-Tert Butyl Ether) or ETBE (Ethyl-Tert Butyl Ether) into a fractionation area and obtaining a stream of high-purity MTBE or ETBE; and the following areas in sequence:
 a fractionation area for obtaining the stream of high-purity MTBE or ETBE; 
 a cracking area of said stream of MTBE or ETBE for obtaining an outgoing stream containing isobutene and the relative alcohol, methanol or ethanol; 
 a washing area with water of the stream leaving the cracking area for the recovery of the relative alcohol, in order to obtain a stream containing isobutene, the ether, and light compounds and a stream containing water and relative alcohol, with a relevant fractionation section for separating the washing water to be recycled to the same washing area from the relative alcohol; 
 a fractionation area of the stream containing isobutene, the ether, and light compounds for separating a stream of high-purity isobutene. 
 
     
     
       2. A process for the production of high-purity isobutene which comprises feeding a stream containing MTBE into a fractionation area and obtaining a stream of MTBE having a purity higher than 98% by weight; and the following areas in sequence:
 a fractionation area for obtaining the stream of MTBE having a purity higher than 98% by weight; 
 a cracking area of said stream of MTBE for obtaining an outgoing stream containing methanol and isobutene; 
 a washing area with water of the stream leaving the cracking area for the recovery of the methanol to obtain a stream containing isobutene, MTBE, and light compounds and a stream containing water and methanol, with a relevant fractionation section for separating the washing water to be recycled to the same washing area from the methanol; 
 a fractionation area of the stream containing isobutene, MTBE, and light compounds for separating a stream of high-purity isobutene. 
 
     
     
       3. A process for the production of high-purity isobutene by means of MTBE cracking according to  claim 2 , comprising the following steps:
 feeding a stream containing MTBE to one or more fractionation columns for the purification of the MTBE, separating a stream containing MTBE and lighter compounds of MTBE, a stream of MTBE having a purity higher than 98% by weight, and a stream containing MTBE and heavier compounds of MTBE; 
 feeding the stream of MTBE having a purity higher than 98% by weight to one or more cracking reactors obtaining an outgoing stream consisting of cracking products and non-converted reagents; 
 feeding said outgoing stream consisting of cracking products and non-converted reagents to a washing column with water, separating a stream containing isobutene, MTBE, and light compounds at the head, and a stream containing methanol and water at the bottom, in turn sent to one or more fractionation columns for separating the water, to be recycled to the washing column, from the methanol; 
 feeding the stream separated from the head of the washing column to a fractionation column for separating the isobutene from the MTBE, obtaining a stream containing isobutene and light compounds at the head, and a stream containing MTBE and heavier compounds at the bottom; 
 feeding the stream separated from the head of the fractionation column containing isobutene and light compounds to another fractionation column for the purification of the isobutene, obtaining a stream containing light compounds at the head and a stream of high-purity isobutene at the bottom. 
 
     
     
       4. The process according to  claim 3 , wherein the stream at the bottom of the washing column containing methanol and water is sent to a single fractionation column, separating a stream containing methanol at the head, and water recycled to the washing column at the bottom. 
     
     
       5. The process according to  claim 3 , wherein the stream at the bottom of the washing column containing methanol and water is sent to a first fractionation column, separating high-octane mixtures (HOM) containing alcohols and ethers at the head and a stream of water and methanol at the bottom, which is sent to a second fractionation column, separating a stream of high-purity methanol at the head, and the water recycled to the washing column at the bottom. 
     
     
       6. The process according to  claim 3 , wherein the stream containing MTBE at the bottom of the fractionation column for separating the isobutene from the MTBE is recycled to the fractionation column(s) for purifying the MTBE. 
     
     
       7. The process according to  claim 5 , wherein a stream, recycled to the cracking reactor(s), is also removed laterally from the second fractionation column of the stream of water and methanol. 
     
     
       8. An integrated process for the production of MTBE or ETBE and high-purity isobutene, starting from streams containing C 4  hydrocarbons, essentially comprising the following areas in sequence:
 a fractionation area for obtaining a stream of high-purity MTBE or ETBE; 
 a cracking area of said stream of MTBE or ETBE for obtaining an outgoing stream containing isobutene and the relative alcohol, methanol or ethanol; 
 a washing area with water of the stream leaving the cracking area for the recovery of the relative alcohol, in order to obtain a stream containing isobutene, the ether, and light compounds, and a stream containing water and relative alcohol, with a relevant fractionation section for separating the washing water to be recycled to the same washing area from the relative alcohol; 
 a fractionation area of the stream containing isobutene, the ether, and light compounds, for separating a stream of high-purity isobutene, 
 further integrated by the following areas: 
 an etherification area fed by streams containing C 4  hydrocarbons and the relative alcohol to obtain the stream containing the ether obtained, C 4  hydrocarbons, and the relative alcohol to be fed to the same fractionation area for obtaining the stream of high-purity MTBE or ETBE; 
 a possible additional etherification area with a relevant fractionation section, for separating a stream containing C 4  hydrocarbons and the relative alcohol and a stream containing the ether obtained, C 4 hydrocarbons, and the relative alcohol to be fed to the first fractionation section; 
 a washing area with water of said stream containing C 4  hydrocarbons and the relative alcohol, coming from the fractionation area, to obtain the stream of high-purity ether, MTBE or ETBE, or from the fractionation section of the possible additional etherification area, with a relevant fractionation section, for separating the washing water to be recycled to the same washing area, 
 said relevant fractionation section for separating the washing water being the same relevant fractionation section of the washing water of the stream leaving the cracking area for separating the stream containing isobutene. 
 
     
     
       9. The integrated process according to  claim 8 , for the production of MTBE and high-purity isobutene, starting from streams containing C 4  hydrocarbons, essentially comprising:
 a fractionation area for obtaining a stream of MTBE having a purity higher than 98% by weight, 
 a cracking area of said stream of MTBE for obtaining an outgoing stream containing methanol and isobutene, 
 a washing area with water of the stream leaving the cracking area for the recovery of the methanol to obtain a stream containing isobutene, MTBE, and light compounds and a stream containing water and methanol, with a relevant fractionation section for separating the washing water to be recycled to the same washing area from the methanol, and 
 a fractionation area of the stream containing isobutene, MTBE, and light compounds for separating a stream of high-purity isobutene; 
 integrated by the following areas: 
 an etherification area fed by streams containing C 4  hydrocarbons and methanol to obtain a stream containing MTBE, C 4  hydrocarbons, and methanol to be fed to the same fractionation area for obtaining the stream of MTBE having a purity higher than 98% by weight; 
 a possible additional etherification area with a relevant fractionation section, for separating a stream containing C 4  hydrocarbons and methanol and a stream containing MTBE, C 4  hydrocarbons and methanol to be fed to the first fractionation section; 
 a washing area with water of said stream containing C 4  hydrocarbons and methanol, coming from the fractionation area, to obtain the stream of MTBE having a purity higher than 98% by weight, or from the fractionation section of the possible additional etherification area, with a relevant fractionation section, for separating the washing water to be recycled to the same washing area, 
 said relevant fractionation section for separating the washing water being the same relevant fractionation section of the washing area of the stream leaving the cracking area for separating the stream containing isobutene. 
 
     
     
       10. The integrated process according to  claim 9 , essentially comprising the steps of:
 feeding a stream containing MTBE to one or more fractionation columns for the purification of the MTBE, separating a stream containing MTBE and lighter compounds of MTBE, a stream of MTBE having a purity higher than 98% by weight, and a stream containing MTBE and heavier compounds of MTBE; 
 feeding the stream of MTBE having a purity higher than 98% by weight to one or more cracking reactors obtaining an outgoing stream consisting of cracking products and non-converted reagents; 
 feeding said outgoing stream consisting of cracking products and non-converted reagents to a washing column with water, separating a stream containing isobutene, MTBE, and light compounds at the head, and a stream containing methanol and water at the bottom, in turn sent to one or more fractionation columns for separating the water, to be recycled to the washing column, from the methanol; 
 feeding the stream separated from the head of the washing column to a fractionation column for separating the isobutene from the MTBE, obtaining a stream containing isobutene and light compounds at the head, and a stream containing MTBE and heavier compounds at the bottom; and 
 feeding the stream separated from the head of the fractionation column containing isobutene and light compounds to another fractionation column for the purification of the isobutene, obtaining a stream containing light compounds at the head and a stream of high-purity isobutene at the bottom; 
 integrated by the following steps: 
 feeding the stream containing C 4  hydrocarbons and methanol to one or more etherification reactors obtaining a stream containing MTBE, C 4  hydrocarbons, and methanol to be fed to the same fractionation column(s) for the purification of the MTBE; 
 feeding the stream containing MTBE and lighter compounds of MTBE, among which C 4  hydrocarbons, separated in the same fractionation column(s) for the purification of MBTE, to an additional washing column with water, separating a stream of C 4  hydrocarbons at the head, and a stream containing methanol and water at the bottom, in turn sent to one or more fractionation columns for separating the water, to be recycled to the washing column, from the methanol, 
 the fractionation column(s) for separating the water from the methanol being the same fractionation column(s) to which the stream at the bottom of the washing column of the stream leaving the cracking reactor, is sent. 
 
     
     
       11. The integrated process according to  claim 9 , essentially comprising the steps of:
 feeding a stream containing MTBE to one or more fractionation columns for the purification of the MTBE, separating a stream containing MTBE and lighter compounds of MTBE, a stream of MTBE having a purity higher than 98% by weight and a stream containing MTBE and heavier compounds of MTBE; 
 feeding the stream of MTBE having a purity higher than 98% by weight to one or more cracking reactors obtaining an outgoing stream consisting of cracking products and non-converted reagents; 
 feeding said outgoing stream consisting of cracking products and non-converted reagents to a washing column with water, separating a stream containing isobutene, MTBE, and light compounds at the head, and a stream containing methanol and water at the bottom, in turn sent to one or more fractionation columns for separating the water, to be recycled to the washing column, from the methanol; 
 feeding the stream separated from the head of the washing column to a fractionation column for separating the isobutene from the MTBE, obtaining a stream containing isobutene and light compounds at the head, and a stream containing MTBE and heavier compounds at the bottom; and 
 feeding the stream separated from the head of the fractionation column containing isobutene and light compounds to another fractionation column for the purification of the isobutene, obtaining a stream containing light compounds at the head and a stream of high-purity isobutene at the bottom; 
 integrated by the following steps: 
 feeding the stream containing C 4  hydrocarbons and methanol to one or more etherification reactors obtaining a stream containing MTBE, C 4  hydrocarbons, and methanol to be fed to the same fractionation column(s) for the purification of MTBE; 
 feeding the stream containing MTBE and lighter compounds of MTBE, among which C 4  hydrocarbons, separated in the same fractionation column(s) for the purification of MBTE, to another etherification reactor(s) obtaining a further stream containing MTBE, C 4  hydrocarbons, and methanol; 
 feeding the further stream containing MTBE, C 4  hydrocarbons, and methanol to another fractional column obtaining a stream containing C 4  hydrocarbons and methanol at the head and a stream containing MTBE at the bottom, which is recycled to the fractionation column for the purification of the MTBE; 
 feeding the stream at the head containing C 4  hydrocarbons and methanol to a further washing column with water, separating a stream of C 4  hydrocarbons at the head, and a stream containing methanol and water at the bottom, in turn sent to one or more fractionation columns for separating the water, to be recycled to the washing column, from the methanol, 
 the fractionation column(s) for separating the water from the methanol being the same fractionation column(s) to which the stream at the bottom of the washing column of the stream leaving the cracking reactor, is sent. 
 
     
     
       12. The process according to  claim 10 , wherein the purification of the MTBE is effected in a single fractionation column. 
     
     
       13. The process according to  claim 3 , wherein the fractionation column for the purification of the MTBE operates at a pressure ranging from 1 to 12 bar g . 
     
     
       14. The process according to  claim 3 , wherein the cracking reactor(s) operate at a temperature ranging from 100 to 300° C., at a pressure ranging from 1 to 10 bar g . 
     
     
       15. The process according to  claim 3 , wherein the washing column of the stream leaving the cracking reactor(s) operates at a temperature ranging from 20 to 100° C., at a pressure ranging from 2 to 15 bar g . 
     
     
       16. The process according to  claim 3 , wherein the fractionation column for the separation of isobutene from the MTBE operates at a pressure ranging from 2 to 10 bar g . 
     
     
       17. The process according to  claim 3 , wherein the fractionation column for the purification of isobutene operates at a pressure ranging from 2 to 15 bar g . 
     
     
       18. The process according to  claim 3 , wherein the fractionation column(s) of the stream containing methanol and water coming from the bottom of the washing column, operate at pressures ranging from atmospheric pressure to 10 bar g . 
     
     
       19. The process according to  claim 10 , wherein the etherification reactor(s) operate in liquid phase. 
     
     
       20. The process according to  claim 19 , wherein the etherification reactor(s) operate at temperatures ranging from 20 to 150° C., and at a pressure below 50 bar g . 
     
     
       21. The process according to  claim 10 , wherein the further washing column of the stream containing C 4  hydrocarbons and methanol operates at a temperature ranging from 20 to 100° C., and at a pressure ranging from 2 to 30 bar g .